Active matrix type organic electroluminescent display device and method of manufacturing the same

ABSTRACT

Disclosed are an active matrix type organic electroluminescent display device and a manufacturing method thereof. At least two capacitors having different functions from each other are disposed in a vertically stacked structure within a unit pixel region. When a compensation circuit needing two or more capacitors having different functions from each other per pixel is applied, the two or more capacitors are vertically stacked, thereby preventing the aperture ratio from being lowered due to the increase in the number of capacitors within the pixel.

TECHNICAL FIELD

The present invention relates to an active matrix type organicelectroluminescent display (AMOLED) device and method of manufacturingthe same, and more particularly, to an AMOLED device and a method ofmanufacturing the same capable of preventing the aperture ratio frombeing lowered when compensation circuits needing two or more capacitorsper pixel are applied.

BACKGROUND ART

In the information society of these days, electronic display devices aremore important as information transmission media and various electronicdisplay devices are widely applied for industrial apparatus or homeappliances. Such electronic display devices are being continuouslyimproved to have new appropriate functions for various demands of theinformation society.

In general, electronic display devices display and transmit variouspieces of information to users who utilize such information. That is,the electronic display devices convert electric information signalsoutputted from electronic apparatus into light information signalsrecognized by users through their eyes.

In the electronic display devices dividing into an emissive displaydevice and a non-emissive display device, the emissive display devicedisplays light information signals through a light emission phenomenathereof and the non-emissive display device displays the lightinformation signals through a reflection, a scattering or aninterference thereof. The emissive display device includes a cathode raytube (CRT), a plasma display panel (PDP), a light emitting diode (LED)and an electroluminescent display (ELD). The emissive display device iscalled as an active display device. Also, the non-emissive displaydevice, called as a passive display device, includes a liquid crystaldisplay (LCD), an electrochemical display (ECD) and an electrophoreticimage display (EPID).

The CRT has been used for a television receiver or a monitor of acomputer as the display device for a long time since it has a highquality and a low manufacturing cost. The CRT, however, has somedisadvantages such as a heavy weight, a large volume and high powerconsumption.

Recently, the demand for a new electronic display device is greatlyincreased such as a flat panel display device having excellentcharacteristics, for example, thin thickness, light weight, low drivingvoltage and low power consumption. Such flat panel display devices canbe manufactured according to the rapidly improved semiconductortechnology.

An electroluminescent (EL) element is attracting attention of interestedperson as one of the flat panel displays. The EL element is generallydivided into an inorganic EL element and an organic EL element dependingon used materials.

The inorganic EL element is a device in which a high electric field isapplied to a light emitting part and electrons are accelerated in theapplied high electric field to collide with a light emitting center, sothat the light emitting center may be exited to emit a light beam.

The organic EL element is a device in which electrons and holes areinjected into a light emitting part from cathode and anode,respectively, and the injected electrons and holes are combined witheach other to generate excitons, thereby emitting light when theseexcitons are transited from an excited state to a base state.

Owing to the above operation mechanism, the inorganic EL element needs ahigh driving voltage of 100-200 V, whereas the organic EL elementoperates at a low voltage of 5-20 V. The above advantage of the organicEL element is activating researches on the organic ELD. Also, theorganic EL element has superior properties such as wide viewing angle,high response speed, high contrast and the like.

The organic EL elements can be applied to both of the active matrix typedisplay device and the passive matrix type display device. The activematrix organic EL display device is a display device that independentlydrives EL elements corresponding to a plurality of pixels usingswitching elements such as a thin film transistor. The organic ELdisplay device is also referred to as an organic electroluminescentdisplay (OELD) device or an organic light emitting device (OLED).Hereinafter, the active matrix organic EL display device is referred toas AMOLED device.

FIG. 1 is an equivalent circuit diagram of a conventional AMOLED device.

Referring to FIG. 1, a unit pixel circuit of a conventional AMOLEDdevice includes two thin film transistors TFT1 and TFT2, and onecapacitor Cst.

Specifically, a plurality of gate lines g1 and g2 and a plurality ofdata lines d1 and d2 are arranged to cross each other, thereby defininga unit pixel region. Between the adjacent data lines d1 and d2, there isarranged a direct current signal line Vdd to be parallel to the datalines d1 and d2. A maximum value of a display signal is applied to theVdd line in the form of direct current.

A first thin film transistor TFT1 as a switching element is connected ata cross point of the gate line g1 and the data line d1. A gate electrodeof the TFT1 is connected to the gate line g1 and a source electrode ofthe TFT1 is connected to the data line d1.

Between a drain electrode of the TFT1 and the Vdd line, there isconnected a storage capacitor Cst. Also, between the drain electrode ofthe TFT1 and the Vdd line, there is connected a second thin filmtransistor TFT2 as a driving element which is in parallel with thestorage capacitor Cst. A gate electrode of the TFT2 is connected to thedrain electrode of the TFT1, a source electrode thereof is connected tothe Vdd line and a drain electrode thereof is connected to an organic ELelement.

If the TFT1 is turned on, the TFT2 is turned on depending on a displaysignal value of the data line d1, so that a direct current signal valueof the Vdd line is applied to the organic EL element, thereby drivingthe organic EL element.

However, in the above AMOLED device to which the circuit using the twoTFTs is applied, there occurs a problem in that brightness of the panelbecomes non-uniform due to a deflection in the characteristics of thedriving TFT, for example, variation in the threshold voltage.

In order to compensate for the deflection in the characteristics of thedriving TFT, there were proposed compensation circuits to which aseparate thin film transistor is added. However, in case that thesecompensation circuits are applied, the number of the thin filmtransistors increases and thus, an area occupied by the thin filmtransistors in a unit pixel region increases to thereby decrease theaperture ratio. Further, since a part of the compensation circuits needstwo capacitors having different functions from each other, the number ofthe thin film transistors and the capacitors arranged in a unit pixelincreases to cause the reduction of the aperture ratio. The reduction inthe aperture ratio lowers the brightness, and requires a high currentdriving so that the life of the circuit is shortened.

DISCLOSURE OF THE INVENTION

Accordingly, it is an object of the present invention to provide anactive matrix type organic electroluminescent display (AMOLED) devicecapable of preventing the aperture ratio from being lowered whencompensation circuits needing two or more capacitors per pixel areapplied.

It is another object of the invention to provide a method formanufacturing an AMOLED device capable of preventing the aperture ratiofrom being lowered when compensation circuits needing two or morecapacitors per pixel are applied.

In one aspect, there is provided an AMOLED in which at least twocapacitors having different functions from each other are disposed in avertically stacked structure within a unit pixel region.

According to another aspect of the invention, there is provided anAMOLED in which a unit pixel is defined by first and second gate linesextending in a first direction, and a data line and a direct currentsignal line extending in a second direction perpendicular to the firstdirection. A first thin film transistor has a first gate electrodeconnected to the first gate line and a first source electrode connectedto the data line. A second thin film transistor has a second gateelectrode connected to the second gate line. A third thin filmtransistor has a third source electrode connected to the direct currentsignal line. An organic EL element is connected between a third drainelectrode of the third thin film transistor and a ground terminal. Afirst capacitor includes a first electrode and a second electrode, thefirst electrode being connected to a third gate electrode of the thirdthin film transistor and a second source electrode of the second thinfilm transistor, and the second electrode being connected to a drainelectrode of the first thin film transistor. A second capacitor includesa third electrode connected to the second electrode and the directcurrent signal line. The first and second capacitors are formed in avertically stacked structure, and have different functions from eachother.

In a further another aspect of an AMOLED according to the presentinvention, a unit pixel is defined by first and second gate linesextending in a first direction, and a data line and a direct currentsignal line extending in a second direction perpendicular to the firstdirection. A first thin film transistor includes a first active patterndisposed adjacent to a cross point of the first gate line and the dataline, a first gate electrode prolonged from the first gate line andcrossing over the first active pattern, a first source electrodeprolonged from the data line and connected to the first active patternat one side of the first gate electrode, and a first drain electrodeconnected to the first active pattern at the other side of the firstgate electrode. A second thin film transistor includes a second activepattern disposed adjacent to a cross point of the second gate line andthe data line, a second gate electrode prolonged from the second gateline and crossing over the second active pattern, a second sourceelectrode connected to the second active pattern at one side of thesecond gate electrode, and a second drain electrode connected to thesecond active pattern at the other side of the second gate electrode. Athird thin film transistor includes a third active pattern disposedwithin the unit pixel, a third gate electrode passing over the thirdactive pattern, a third source electrode prolonged from the directcurrent signal line and connected to the third active pattern at oneside of the third gate electrode, and a third drain electrode prolongedfrom the second drain electrode and connected to the third activepattern at the other side of the third gate electrode. A first capacitorincludes a first electrode and a second electrode. The first electrodeis prolonged from the second active pattern and disposed parallel to thedirect current signal line below the direct current signal line. Thesecond electrode is formed on the first electrode and connected to thefirst drain electrode. A second capacitor includes the second electrodeand a third electrode formed on the second electrode. The thirdelectrode is connected to the direct current signal line. The secondcapacitor has a different function from that of first capacitor. A pixelelectrode connected to the third drain electrode is disposed within theunit pixel.

In a method of manufacturing an AMOLED according to the presentinvention, a first electrode and active patterns are formed on each ofpixel regions on a substrate. A gate insulating layer is formed on theactive patterns, the first electrode and the substrate. First, secondand third gate electrodes are formed on a gate insulating layer abovethe active pattern and a second electrode is formed on the gateinsulating layer above the first electrode to form a first capacitorincluding the first electrode, the gate insulating layer and the secondelectrode. An insulating interlayer is formed on the first, second andthird gate electrodes, the second electrode and the gate insulatinglayer. First, second and third source electrodes, and first, second andthird drain electrodes are formed on the insulating interlayer above theactive pattern to form a first thin film transistor including the firstgate electrode, the first source electrode and the first drainelectrode, a second thin film transistor including the second gateelectrode, the second source electrode and the second drain electrode,and a third thin film transistor including the third gate electrode, thethird source electrode and the third drain electrode. At the same time,a third electrode is formed on the insulating interlayer above the firstelectrode to form a second capacitor vertically stacked on the firstcapacitor and including the second electrode, the insulating interlayerand the third electrode. A passivation layer is formed on the first,second and third thin film transistors, the first and second capacitorsand the insulating interlayer. A pixel electrode is formed on thepassivation layer. An organic EL element is formed on the pixelelectrode.

According to the present invention, when compensation circuits needingtwo or more capacitors having different functions from each other perpixel are applied, the capacitors are stacked in a vertical direction tothereby prevent the aperture ratio from being lowered due to theincrease in the number of the capacitors in the pixel.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and other advantages of the present invention willbecome more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a circuit diagram of a conventional AMOLED device;

FIG. 2 is a plan view of an AMOLED device in accordance with oneembodiment of the present invention;

FIG. 3 is an equivalent circuit diagram of FIG. 2;

FIG. 4 is a cross-sectional view taken along the line A-A′ of FIG. 2;and

FIGS. 5A to 5E are cross-sectional views for illustrating a method ofmanufacturing the AMOLED device shown in FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, exemplary embodiments of the present invention will be described indetail with reference to the annexed drawings.

FIG. 2 is a plan view of an AMOLED device in accordance with oneembodiment of the present invention, FIG. 3 is an equivalent circuitdiagram of FIG. 2, and FIG. 4 is a cross-sectional view taken along theline A-A′ of FIG. 2.

Referring to FIGS. 2 to 4, a unit pixel circuit of an AMOLED inaccordance with the present invention includes three thin filmtransistors T1, T2 and T3, two capacitors C1 and C2, and fourinterconnection lines GL1, GL2, D1 and Vdd.

Particularly, a unit pixel is defined by first and second gate lines GL1and GL2 extending in a first direction and a data line DL and a directcurrent signal line Vdd extending in a second direction perpendicular tothe first direction.

The first gate line GL1 plays a role of turning on/off the first thinfilm transistor T1 as a switching element to thereby apply an initialdata voltage and a gray level voltage through the data line DL. Thesecond gate line GL2 plays a role of turning on/off the second thin filmtransistor T2 to thereby compensate the characteristics of the thirdthin film transistor T3 as a driving element. A maximum value of thedisplay signal is constantly applied to the direct current signal lineVdd in a direct current state.

The first thin film transistor T1 includes a first active pattern 105disposed adjacent to a cross point of the first gate line GL1 and thedata line DL, a first gate electrode 110 prolonged from the first gateline GL1 and crossing over the first active pattern 105, a first sourceelectrode 122 prolonged from the data line DL and connected to the firstactive pattern 105 at one side (a first side) of the first gateelectrode 110, and a first drain electrode 123 connected to the firstactive pattern 105 at the other side (a second side that is opposite tothe first side) of the first gate electrode 110. The first gateelectrode 110 of the first thin film transistor T1 is connected to thefirst gate line GL1 and the first source electrode 122 thereof isconnected to the data line DL.

The second thin film transistor T2 includes a second active pattern 106disposed adjacent to a cross point of the second gate line GL2 and thedata line DL, a second gate electrode 111 prolonged from the second gateline GL2 and crossing over the second active pattern 106, a secondsource electrode 125 connected to the second active pattern 106 at oneside of the second gate electrode 111, and a second drain electrode 124connected to the second active pattern 106 at the other side of thesecond gate electrode 111. The second gate electrode 111 of the secondthin film transistor T2 is connected with the second gate line GL2.

The third thin film transistor T3 includes a third active pattern 107disposed within the unit pixel, a third gate electrode 112 crossing overthe third active pattern 107, a third source electrode 127 prolongedfrom the direct current signal line Vdd and connected to the thirdactive pattern 107 at one side of the third gate electrode 112, and athird drain electrode 126 prolonged from the second drain electrode 124and connected to the third active pattern 107 at the other side of thethird gate electrode 112. The third gate electrode 112 of the third thinfilm transistor T3 is connected with the second source electrode 125 ofthe second thin film transistor T2, the third source electrode 127thereof is connected with the direct current signal line Vdd, and thethird drain electrode 126 thereof is connected with the second drainelectrode 124 of the second thin film transistor T2 and an organic ELelement.

Preferably, the third thin film transistor T3 is in a p-type, and thefirst and second thin film transistors T1 and T2 are in either n-type orp-type.

The first capacitor C1 includes a first electrode 108, a gate insulatinglayer 109 and a second electrode 113. The first electrode 108 isprolonged from the second active pattern 106 of the second thin filmtransistor T2 and disposed parallel to the direct current signal lineVdd below the direct current signal line Vdd. The second electrode 113is overlapped with the first electrode 108. The first electrode 108 isformed from the same layer as in the active patterns 105, 106 and 107 ofthe first, second and third thin film transistors T1, T2 and T3. Thesecond electrode 113 is formed from the same layer as in the gate lineGL. The first electrode 108 of the first capacitor C1 is connected withthe third gate electrode 112 of the third thin film transistor T3 andthe second source electrode 125 of the second thin film transistor T3.The second electrode 113 of the first capacitor C1 is connected with thefirst drain electrode 123 of the first thin film transistor T1. Thefirst capacitor C1 functions to store a voltage compensating for thecharacteristics of the third thin film transistor T3 and to transfer adata voltage to the third gate electrode 112 of the third thin filmtransistor T3.

The second capacitor C2 includes the second electrode 113, an insulatinginterlayer layer and a third electrode 128 overlapped with the secondelectrode 113. The third electrode 128 of the second capacitor C2 isconnected to the direct current signal line Vdd.

The third electrode 128 is formed from the same layer as in the dataline DL. The second capacitor C2 is connected between the direct currentsignal line Vdd and the first drain electrode 123 of the first thin filmtransistor T1. The second capacitor C2 functions to maintain the datavoltage at a constant level during a frame time.

Accordingly, the first capacitor C1 and the second capacitor C2 have adifferent function from each other. While sharing a common electrode,i.e., the second electrode 113 connected to the first drain electrode123 of the first thin film transistor T1, the first and secondcapacitors C1 and C2 are formed in a stacked structure in a verticaldirection.

Within a unit pixel region of the present invention, there is formed apixel electrode 134 connected to the third drain electrode 126 of thethird thin film transistor T3. Also, a fourth electrode 135 formed fromthe same layer as in the pixel electrode 134 is formed to be overlappedwith the third electrode 128 of the second capacitor C2. When it isrequested that the second capacitor C2 has a high capacitance, theinsulating interlayer 114 and the passivation layer 130 disposed betweenthe second electrode 113 and the fourth electrode 135 serve as adielectric layer of the capacitor, thereby securing a necessarycapacitance.

The pixel circuit of the present invention operates as follows.

If the first thin film transistor T1 is turned on by the first gate lineGL1, the third thin film transistor T3 is turned on according to adisplay signal value of the data line DL, so that a direct currentsignal value of the direct current signal line Vdd is applied to theorganic EL element to thereby drive the organic EL element. At thistime, if a compensation voltage is applied to the second gate line GL2to turn on the second thin film transistor T2, the third gate electrode112 and the third drain electrode 126 of the third thin film transistorT3 are connected to each other, so that a difference in thecharacteristics of the third thin film transistor T3 as a drivingelement is reduced.

Hereinafter, there is described a method of manufacturing the AMOLEDhaving the aforementioned structure in accordance with the presentinvention.

FIGS. 5A to 5E are cross-sectional views for illustrating the AMOLEDshown in FIG. 4.

Referring to FIG. 5A, on an insulating substrate 100 such as glass,quartz or sapphire, silicon oxide is deposited to a thickness of anapproximately 2,000 Å by a plasma-enhanced chemical vapor deposition(PECVD), to form a blocking layer 101. The blocking layer 101 ispreferably used to prevent heat loss during a subsequent crystallizationprocess of an amorphous silicon film.

An n-type doped amorphous silicon is deposited to a thickness of about800 Å by the PECVD on the blocking layer 101, and then, patterned usinga photolithography process to form buffer layers 102 and 103 on a thinfilm transistor region and a capacitor region within the unit pixel.

Thereafter, on the buffer layers 102 and 103 and the blocking layer 101,an amorphous silicon is deposited to a thickness of about 500 Å by a lowpressure chemical vapor deposition (LPCVD) or a PECVD method to therebyform an active layer 104. Then, a laser annealing or a furnace annealingis carried out to crystallize the active layer 104 into apolycrystalline silicon layer.

Referring to FIG. 5B, through a photolithography process, thepolycrystalline silicon active layer 104 is patterned to form a firstactive pattern (105 in FIG. 2), a second active pattern (106 in FIG. 2)and a third active pattern 107 on the thin film transistor region withinthe unit pixel. At the same time, a first electrode 108 made of thepolycrystalline silicon active layer is formed on the capacitor regionwithin the unit pixel.

Then, on the entire surface of the resultant structure on which theactive patterns 105, 106 and 107 and the first electrode 108 are formed,silicon oxide is deposited to a thickness of about 1000-2000 Å by thePECVD method, thereby forming a gate insulating layer 109.

Referring to FIG. 5C, on the gate insulating layer 109, a gate layersuch as AlNd is deposited to a thickness of approximately 3000 Å by asputtering method. Then, the gate layer is patterned via aphotolithography process. As a consequence, there are formed first andsecond gate lines (GL1 and GL2 in FIG. 2) extending in a firstdirection, a first gate electrode (110 in FIG. 2) of the first thin filmtransistor T1 branched from the first gate line GL1, a second gateelectrode (111 in FIG. 2) of the second thin film transistor T2 branchedfrom the second gate line GL2, a third gate electrode 112 of the thirdthin film transistor T3 arranged within the unit pixel. At the sametime, the second electrode 113 made from the gate layer is formed to beoverlapped with the first electrode 108. The second electrode 113 isused as a common electrode of the stack type first and second capacitorsC1 and C2.

Then, by performing an impurity ion implantation using a photo mask usedin the patterning process of the gate layer, source/drain regions (notshown) of the first, second and third thin film transistors T1, T2 andT3 are formed. Preferably, the third thin film transistor T3 is inp-type, and the first and second thin film transistors T1 and T2 are inn-type or p-type.

Referring to FIG. 5D, in order to activate the doped ions in the sourceand drain regions and cure damages of the silicon layer, a laserannealing or a furnace annealing is performed. Then, silicon nitride isdeposited on the entire surface of the resultant structure to athickness of approximately 8,000 Å to thereby form an insulatinginterlayer 114.

Thereafter, the insulating interlayer 114 is etched by aphotolithography process to form contact holes 115, 116, 117, 118, 119and 120 exposing the source/drain regions of the first, second and thirdthin film transistors T1, T2 and T3. At this time, a contact hole 121exposing a predetermined portion of the third gate electrode 112 of thethird thin film transistor T3 is also formed.

A data layer such as MoW or AlNd layer is deposited on the contact holes115, 116, 117, 118, 119, 120 and 121 and the insulating interlayer 114to a thickness of about 3000-6000 Å, and then, patterned by aphotolithography process. As a consequence, there are formed a data lineDL and a direct current signal line Vdd which are extended in a seconddirection perpendicular to the first direction, first source/drainelectrodes (122 and 123 of FIG. 2) of the first thin film transistor T1,second source/drain electrodes (125 and 124 of FIG. 2) of the secondthin film transistor T2, and third source/drain electrodes 127 and 126of the third thin film transistor T3, which are connected to thesource/drain regions through the contact holes. At the same time, thethird electrode 128 made from the data layer is formed to be overlappedwith the second electrode 113. The third electrode 128 is comprised ofthe direct current signal line Vdd, and connected to the third sourceelectrode 127 of the third thin film transistor T3. Preferably, using asingle electrode pattern, the second drain electrode 124 of the secondthin film transistor T2 and the third drain electrode 126 of the thirdthin film transistor T3 are formed at the same time. Also, the secondsource electrode 125 of the second thin film transistor T2 is formed tomake contact with the third gate electrode 112 of the third thin filmtransistor T3.

Referring to FIG. 5E, silicon nitride is deposited on the data line DL,the direct current signal line Vdd, the source/drain electrodes 122,123, 124, 125, 126 and 127 and the insulating interlayer 130 to athickness of approximately 2000-3000 Å to form a passivation layer 130.Thereafter, the passivation layer 130 is etched away using aphotolithography process to form a via hole 132 exposing the third drainelectrode 126 of the third thin film transistor T3.

A transparent conductive layer such as indium tin oxide (ITO) or indiumzinc oxide (IZO) is deposited to a thickness of approximately 300-500 Åon the via hole 132 and the passivation layer 130, and then, patternedby a photolithography process. By doing so, a pixel electrode 134 isformed to be connected with the third drain electrode 126 of the thirdthin film transistor T3 through the via hole 132. At the same time, afourth electrode 135 made of the transparent conductive layer is formedto be overlapped with the third electrode 128.

As shown in FIG. 4, after forming an organic insulating layer 136 on thepixel electrode 134, the fourth electrode 135 and the passivation layer130, the organic insulating layer 136 is exposed and developed tothereby form an opening 137 having the same shape as the pixel electrode134. Preferably, the opening 137 is formed to have a width smaller thanthat of the pixel electrode 134.

Then, a hole transfer layer (HTL) 138, a luminescent layer 140 and anelectron transfer layer (ETL) 142 are sequentially formed on the opening137 and the organic insulating layer 136. A cathode electrode 144 isformed thereon to thereby complete an organic EL element.

As described above, according to the present invention, when acompensation circuit needing two or more capacitors having differentfunctions from each other per pixel is applied, the two or morecapacitors are vertically stacked, thereby preventing the aperture ratiofrom being lowered due to the increase in the number of capacitorswithin the pixel.

Also, it is apparent that a stack type capacitor of the invention can beapplied to any other pixel circuits using two or more capacitors havingdifferent functions from each other.

While the present invention has been described in detail, it should beunderstood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended claims.

1. An active matrix type organic electroluminescent display devicecomprising: a data line extended in a first direction; a first gate lineextended in a second direction different from the first direction; afirst thin film transistor (TFT) including a gate electrode connected tothe first gate line, a source electrode connected to the data line and adrain electrode; a first capacitor including a first electrode and asecond electrode; a second capacitor including the second electrode anda third electrode; a second TFT including a gate electrode connected tothe first capacitor, a source electrode connected to the secondcapacitor and a drain electrode; and an organic electroluminescentelement connected to the drain electrode of the second TFT, wherein thefirst and second capacitors are disposed in a vertically stackedstructure within a unit pixel region and the drain electrode of thefirst TFT is connected between the first capacitor and the secondcapacitor.
 2. The active matrix type organic electroluminescent displaydevice as claimed in claim 1, wherein the drain electrode of the firstTFT is connected to the second electrode of the first and secondcapacitors.
 3. The active matrix type organic electroluminescent displaydevice as claimed in claim 2, further comprising a second gate lineextended in the second direction and a direct current signal lineextended in the first direction.
 4. The active matrix type organicelectroluminescent display device as claimed in claim 3, wherein thesecond capacitor is connected to the direct current signal line.
 5. Theactive matrix type organic electroluminescent display device as claimedin claim 4, further comprising a third TFT having a gate electrodeconnected to the second gate line, a source electrode connected to thegate electrode of the second TFT and a drain electrode connected to thedrain electrode of the second TFT.
 6. The active matrix type organicelectroluminescent display device as claimed in claim 1, wherein thesource electrode of the second TFT is connected to the third electrodeof the second capacitor.
 7. An active matrix type organicelectroluminescent display device in which a unit pixel is defined byfirst and second gate lines extending in a first direction, and a dataline and a direct current signal line extending in a second directionperpendicular to the first direction, said active matrix type organicelectroluminescent display device comprising: a first thin filmtransistor having a first gate electrode connected to the first gateline and a first source electrode connected to the data line; a secondthin film transistor having a second gate electrode connected to thesecond gate line; a third thin film transistor having a third sourceelectrode connected to the direct current signal line; an organicelectroluminescent element connected between a third drain electrode ofthe third thin film transistor and a ground terminal; a first capacitorincluding a first electrode and a second electrode, the first electrodebeing connected to a third gate electrode of the third thin filmtransistor and a second source electrode of the second thin filmtransistor, and the second electrode being connected to a first drainelectrode of the first thin film transistor; and a second capacitorincluding the second electrode and a third electrode connected to thedirect current signal line, wherein the first and second capacitors areformed in a vertically stacked structure and have different functionsfrom each other.
 8. An active matrix type organic electroluminescentdisplay device in which a unit pixel is defined by first and second gatelines extending in a first direction, and a data line and a directcurrent signal line extending in a second direction perpendicular to thefirst direction, the active matrix type organic electroluminescentdisplay device comprising: a first thin film transistor including afirst active pattern disposed adjacent to a cross point of the firstgate line and the data line, a first gate electrode prolonged from thefirst gate line and crossing over the first active pattern, a firstsource electrode prolonged from the data line and connected to the firstactive pattern at a first side of the first gate electrode, and a firstdrain electrode connected to the first active pattern at a second sideof the first gate electrode; a second thin film transistor including asecond active pattern disposed adjacent to a cross point of the secondgate line and the data line, a second gate electrode prolonged from thesecond gate line and crossing over the second active pattern, a secondsource electrode connected to the second active pattern at a first sideof the second gate electrode, and a second drain electrode connected tothe second active pattern at a second side of the second gate electrode;a third thin film transistor including a third active pattern disposedwithin the unit pixel, a third gate electrode crossing over the thirdactive pattern, a third source electrode prolonged from the directcurrent signal line and connected to the third active pattern at a firstside of the third gate electrode, and a third drain electrode prolongedfrom the second drain electrode and connected to the third activepattern at a second side of the third gate electrode; a first capacitorincluding a first electrode and a second electrode, the first electrodebeing prolonged from the second active pattern and disposed parallel tothe direct current signal line below the direct current signal line, andthe second electrode being formed on the first electrode and connectedto the first drain electrode; a second capacitor including the secondelectrode and a third electrode formed on the second electrode, thethird electrode being connected to the direct current signal line, thesecond capacitor having a different function from that of the firstcapacitor; and a pixel electrode disposed within the unit pixel so as tobe connected to the third drain electrode.
 9. The active matrix typeorganic electroluminescent display device as claimed in claim 8, whereinthe first electrode, and the first, second and third active patterns areformed from a same layer.
 10. The active matrix type organicelectroluminescent display device as claimed in claim 8, wherein thesecond electrode and the gate line are formed from a same layer.
 11. Theactive matrix type organic electroluminescent display device as claimedin claim 8, wherein the third electrode and the data line are formedfrom a same layer.
 12. The active matrix type organic electroluminescentdisplay device as claimed in claim 8, further comprising a fourthelectrode formed from a same layer as in the pixel electrode on thedirect current signal line.
 13. The active matrix type organicelectroluminescent display device as claimed in claim 8, wherein thesecond source electrode of the second thin film transistor is connectedwith the third gate electrode of the third thin film transistor.
 14. Amethod of manufacturing an active matrix type organic electroluminescentdisplay device, the method comprising the steps of: forming an activepattern and a first electrode in a pixel region of a substrate; forminga gate insulating layer on the active pattern, the first electrode andthe substrate; forming first, second and third gate electrodes on thegate insulating layer above the active pattern and simultaneously,forming a second electrode on the gate insulating layer above the firstelectrode to form a first capacitor including the first electrode, thegate insulating layer and the second electrode; forming an insulatinginterlayer on the first, second and third gate electrodes, the secondelectrode and the gate insulating layer; forming first, second and thirdsource electrodes, and first, second and third drain electrodes on theinsulating interlayer above the active patterns to form a first thinfilm transistor including the first gate electrode, the first sourceelectrode and the first drain electrode, a second thin film transistorincluding the second gate electrode, the second source electrode and thesecond drain electrode, and a third thin film transistor including thethird gate electrode, the third source electrode and the third drainelectrode, and simultaneously, to form a third electrode on theinsulating interlayer above the first electrode to form a secondcapacitor vertically stacked on the first capacitor and including thesecond electrode, the insulating interlayer and the third electrode;forming a passivation layer on the first, second and third thin filmtransistors, the first and second capacitors and the insulatinginterlayer; forming a pixel electrode on the passivation layer; andforming an organic electroluminescent element on the pixel electrode.15. The method as claimed in claim 14, wherein the second drainelectrode of the second thin film transistor and the third drainelectrode of the third thin film transistor are formed from a singleelectrode pattern.
 16. The method as claimed in claim 14, wherein thesecond source electrode of the second thin film transistor is formed tomake contact with the third gate electrode of the third thin filmtransistor.
 17. The method as claimed in claim 14, wherein a fourthelectrode is formed to be overlapped with the third electrode in thestep of forming the pixel electrode.